1. Field of the Invention
The invention relates to products having operator-access covers which protect operators from dangerous machine elements (rotating hardware, moving parts, etc.) but which need to be regularly opened by operators for service access and maintenance.
2. Background Art
The use of an interlock actuator for an operator-access cover is required in certain applications. Such operator-access covers are required, as a matter of product design requirements and/or regulatory standards, to incorporate some automatic interlock feature which will de-energize any dangerous machine element when the cover is opened and render the exposed parts of the machine safe for operator access. Such interlock function is usually provided by an electrical switch or switches, which break the supply of electrical power to the exposed machinery and/or send a signal to the controlware of the machine, which in turn breaks the power supply and/or otherwise renders the machinery safe.
Such electrical switches are typically highly regulated as to type and construction by the regulatory agencies who specify interlock functions and certify compliance. Switches, for example, must typically be double-pole, of approved construction and contact separation, non-defeatable without the use of special tools (incapable of being “cheated”) and self-resetting when overridden for service. One consequence of these regulatory requirements is that such switches typically have a very narrow range of motion in which they are guaranteed to operate. For example, a plunger switch may have a range of plunger motion in which the maker guarantees correct closed contact configuration of +/−0.015 inches.
Such operator-access covers are typically hinged to open and close. Workers in the art are aware of the great difficulty of mounting and configuring such switches to ensure reliable operation (given their narrow operating range) while still making covers, hinge systems and the like within normal manufacturing tolerances. It is very easy for normal manufacturing tolerances to accumulate through the various parts of the cover, hinges and switch mounts to the point where the operating range of the switch is exceeded by the possible range of tolerances in the various parts. For this reason, switches are often actuated through a separate adjustable actuator, which can be adjusted to compensate for tolerance accumulation.
Leaving aside the added cost, such adjustable actuators are less-than-desirable because it is virtually impossible to ensure that they are adjusted to actuate the switch fully. In other words, the actuator may be adjusted so that the switch is seen to work correctly (as tested by electrical measurement, for example) but there is no practical way to tell whether the switch is at one limit or the other of its operating range, and liable to fail at any time due to part variation, vibration or the slightest change in the intervening parts. Another problem is that of over-travel—where the actuator is adjusted so that it over-actuates the switch, causing unacceptable pressures on the switch assembly and poor fit or closure of the cover. Such switches and adjustable actuators are a continual source of service attention and unplanned downtime.
For the foregoing reasons, there is a need for an improved interlock actuator for a hinged cover.